1. Field
The present invention relates to a stator assembly structure for an axial flux electric machine, and more particularly, to an architecture of a junction surface of the stator and the disk-type stator seat formed with at least one tooth-like engagement structure; the stator manufactured by cutting or punching a silicon steel easily produces concave grooves or convex teeth on the axial surface of the stator; no matter whether the disk-type stator seat is made of a metal material such as Al or Mg by casting or a non-metallic material with good thermal conductivity such as an engineering plastic by mold forming, the stator of the present invention has the junction surface with the tooth-like structure like a groove channel that allows the liquid disk-type stator seat material to flow easily so as to enable the stator and the disk-type stator seat made of different materials to be integrated more easily by casting or mold forming, and the tooth-like structure enables the junction surface to bear a larger rotation stress.
2. Related Art
Along with the progress of the rare earth material science, a permanent magnet of a very small volume may generate a very large magnetic torque, so that the research and development direction of the electric machine is increasingly developed towards the high-power density. In other words, the power generated in the unit volume and weight becomes larger, so the electromagnetic field generated by the coil needs to improve the power accordingly, that is, the current passing the coil or the voltage on the coil is improved. Generally, the winding of the conventional coil made of a good conductive wire material of a low resistance (such as a copper wire material) still produces a tiny electric impedance. The tiny electric impedance may still produce power loss (i.e. copper loss) under the function of large current, and the copper loss of the coil may be dissipated in the form of heat. If the heat cannot be rapidly transmitted to the outside, the heat is accumulated to cause the increasing of the temperature of the coil and burn-out of the electric insulating coating of the coil. Generally, the coil is wound on a stator and the stator generates an eddy current under the electromagnetic field. The eddy current may generate the power loss in the ferrous material with a relatively high electric impedance (i.e. ferrous loss). The ferrous loss is also dissipated in the form of heat, and although the stator may be fabricated by the silicon steel material to reduce the influence of the eddy current, in the situation of large current direction variance or high frequency, the ferrous loss proportion rises to an extremely large ratio and the heat of the ferrous loss is accumulated on the heat of the copper loss, thus enhancing the overheat phenomenon of the coil. If the heat generated by the copper loss and the ferrous loss cannot be rapidly transmitted to the outside, the temperature accumulated on the coil becomes higher, which may generate a heat shock on the enameled wire of the coil. The high temperature may accelerate the aging and deterioration of the electric insulating coating between the wires of the coil. If the temperature exceeds the temperature that can be endured by the electric insulating coating (generally around 130-160° C.), the electric insulating coating is punched, thus causing the short circuit burn-out and failure of the coil. Therefore, how to improve the heat dissipation capability of the stator assembly becomes the technical key point for the axial flux electric machine of high torque density. Generally, in the prior art, a good thermal conductivity material (such as, Al material) is adopted for manufacturing the disk-type stator seat and a forced air cooling or water cooling method is applied on the disk-type stator seat to enhance the heat dissipation capability of the disk-type stator seat and also enhance the heat dissipation capability of the stator assembly indirectly, which is a good implementation structure.
The heat generated by the stator and the coil is mostly transmitted to the disk-type stator seat from the stator, and is dissipated by the disk-type stator seat in the air cooling or water cooling manner. Since the thermal energy needs to flow through the junction surface between the stator and the disk-type stator seat, if the structure between the stator and the disk-type stator seat does not generate a sufficient contact surface area, the coefficient of thermal conductivity of the junction surface is quite low (i.e. the thermal impedance is very large) so the heat is hard to pass. That is to say, the heat of the copper loss of the coil and the ferrous loss of the stator is difficult to flow to the disk-type stator seat. Even if the disk-type stator seat has a good heat dissipation capability, the entire stator assembly still cannot endure the high power working as the temperature is extremely high. Therefore, it is a crucial technique key to provide a good design of the structure between the stator and the disk-type stator seat.
The conventional method for fabricating the stator assembly is fixing the stator and the disk-type stator seat by a screw-fastening method, a high-performance adhesive attaching method or both. To ensure the air gap between the stator and the rotator, i.e. control the axial size tolerance between the stator and the disk-type stator seat so as to achieve a very high precision and a very smooth surface roughness, the two members are adhered by compression or joined by screw-fastening. Since the stator structure is mostly formed by a plurality of very thin silicon steels stacked together, the stator made of multiple layers of silicon steel material is difficult to be processed by mechanical cutting. Not only the cost is very high, but also the required precision tolerance size and surface roughness cannot be achieved by the contact surface. If the grinding manner is adopted to process and improve the size precision, the cost is higher than the mechanical cutting method, so the grinding method does not meet the economic benefit requirement. Therefore, the major concerns in the prior art include: generating the effective junction surface area between the stator and the disk-type stator seat and not achieving a high proportion of total contact between the two physical bodies. In the micro level, a lot of gaps exist between the stator and the disk-type stator seat. Since the thermal conductivity of the air is poor, the junction surface becomes the interface that prevents the heat of the stator from being transmitted to the stator seat. As the adhesive with high adhesion, high thermal conductivity and high thermal resistance has not been developed, the contact surface area between the stator and the disk-type stator seat is still not large enough. When the conventional method is applied in the high-power electric machine, due to the poor thermal conductivity, the temperature of the coil is too high, thus causing the limitation to the application power, and an axial flux disk electric machine of high-power density cannot be further developed, which is the biggest deficiency in the prior art.
The stator assembly structure of a conventional electric machine may refer to U.S. Pat. No. 6,922,004 B2 (The Timken Company, Canton, Ohio (US)) in FIG. 1, US Patent No. US-2010/0164316A1 (IN MOTION TECHNOLOGIES PTY LIMITED, Dandenong South, VIC (AU)) in FIG. 2, U.S. Pat. No. 3,061,075 (Charles Burchard Stcgman, 5757 Tobias, Van Nuys, Calif. (US)) in FIG. 3, U.S. Pat. No. 5,646,467 (Kollmorgen Corporation, Waltham, Mass. (US)) in FIG. 4. The method for integrally casting the stator and the stator seat has not been disclosed in the prior art. According to the technical contents of FIG. 1, FIG. 2 and FIG. 4, the method of firmly binding the stator and the stator seat has not been disclosed, and also the technique of forming convex or concave tooth-like structures on the stator junction surface to enhance the binding force has not been disclosed. The stator has the conventional nut holes for fixing the stator on the motor casing with screws, so the heat dissipation between the stator and the stator seat is still unsatisfactory. FIG. 3 has not disclosed the technique of forming convex or concave tooth-like structures on the stator junction surface to enhance the binding force. The stator is fixed on the motor stator seat casing by a conventional welding method, so the heat dissipation between the stator and the stator seat is still unsatisfactory and needs modification.
Therefore, it is expected to improve the dissipation of heat of the stator and the coil rapidly to the disk-type stator seat and also enable the stator and the disk-type stator seat to be engaged together to form a firm structure, thereby ensuring the reliability of the machine.
In the present invention, to improve the dissipation of heat of the stator and the coil rapidly to the disk-type stator seat, the coefficient of thermal conductivity between the stator and the disk-type stator seat needs improvement. Under the condition of not increasing the cost, if the stator and the disk-type stator seat are tightly attached, the coefficient of thermal conductivity therebetween can be improved. There are technical difficulties in realizing the good contact state of the junction surface between the stator and the disk-type stator seat, and the best solution is one-piece casting or mold forming of the both. There are also difficulties in casting the stator and the disk-type stator seat together. Particularly, how to firmly bind the junction surfaces of the two members made of different materials is the crucial technique for solving the problems in the conventional stator assembly structure in the present invention.